Movable barriers of various kinds are known, as are powered movable barrier operators that serve to selectively move a corresponding movable barrier between, for example, opened and closed positions. When power is unavailable for any reason, such powered movable barrier operators are ordinarily rendered inoperable. In many cases, when the powered movable barrier operator becomes inoperable, the movable barrier itself cannot be opened. This typically results because the operator itself and/or the linkage between the operator and the movable barrier will inherently resist unpowered movement of the movable barrier.
Such a tendency to resist opening when unpowered can present problems. For example, important access/entry points can be blocked, thereby denying exit to individuals seeking safety during an emergency and/or delaying or prohibiting entry of emergency response personnel who might otherwise be able to present needed aid and assistance. As a result, in some instances, prior art solutions have been made to allow certain movable barriers to be opened even when motive power has been lost.
Many such proposals are not entirely adequate to the task. The operative mechanism may be difficult to operate, expensive to implement, or suitable only for initial (as versus retrofitting) installation applications. Further, some prior art proposals may work satisfactorily when the movable barrier is substantially unloaded, but prove difficult or impossible to operate when the corresponding movable barrier is loaded for some reason (as happens, for example, when a swinging gate is pressing upon a stationary vehicle or vice versa). Yet other proposals may prove overly sensitive to environmental factors and/or ordinary wear and tear.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.